Governments are ramping up online attacks on human rights advocates as the Internet becomes a key battleground for fights against oppression and censorship.

"The cyberwarfare is increasing," Balatarin.com director Mehdi Yahyanejad said Tuesday at an annual Business & Human Rights Summit at the Yahoo! campus in the California city of Sunnyvale.

"If you have a blog or an email on a controversial website you are going to get targeted. Governments understand this is an important issue for them."

Yahyanejad is director of Balatarin.com, a popular Iranian website where people share links to Internet pages they find interesting.

Internet companies such as Google, Microsoft, Yahoo!, Facebook and Twitter are increasingly in cross-hairs of governments bent on stifling criticism and thwarting efforts to organize protests or share news.

Google spotlighted the issue this year when it stopped providing censored Internet results in China in response to attacks by hackers mining the US technology giant for information about human rights activists in that country.

"This was something that Google chose to do based on our code of ethics," company spokesman Scott Rubin said while taking part in a panel at the summit.

"We would love to offer search there but it has to be uncensored."

Conventional threats against people voicing dissent online include hacking of Internet accounts, "distributed denial of service" attacks that overwhelm servers with requests, and infecting machines with spy viruses.

"As we've seen in the attack on Google and others the fact that you have a highly motivated assailant is not just a vulnerability for human rights it is a vulnerability to your engineering infrastructure," said Danny O'Brien of the Committee to Protect Journalists.

"Unconventional" online attacks include governments using personal information about citizens to impersonate them and seize control of online accounts or domain names by tricking Internet service providers.

Some governments use terms of service at Internet companies to have photos, videos or other content taken down with claims that material is offensive or violent, said AccessNow.com co-founder Kim Pham.

"As more people get on line, governments see the significance of the Internet and try to harness situations," Pham said. "It is in their interest to clamp down. It is inevitable."

YouTube is "slowly rolling out around the world" a system that will let people appeal the removal of videos they have uploaded to the website, according to Rubin.

"Where ever possible we will enable as much expression as we can," Rubin said. "We are working on greater transparency all the time."

US government and Internet representatives that took part in panels at the summit skirted comment regarding Google's decision to put free expression over profit in China's booming market.

A theme at the first summit was Internet giants and rights advocates uniting in a Global Network Initiative (GNI) for solidarity "in the advancement of user rights to freedom of expression and privacy."

Microsoft, Yahoo!, and Google are GNI members.

Google has essentially been left standing alone in its China move, with firms such as US technology colossus Microsoft opting for "engagement" strategies that bow to Internet censorship rules in that country.

Yahoo! has publicly backed Google. Five years ago Yahoo! sold its operations in China to Alibaba.com, taking a stake in the company as part of the deal.

"The decision to pull out of China was entirely our own," Rubin said. "In regard to whether there is ongoing support, it is up to each individual to decide that."

Yahoo! Business & Human Rights Program director Ebele Okobi-Harris contended that the GNI set principles for members and did not dictated courses of action.

"There isn't a monolithic view," Okobi-Harris said. "You would find fair disagreement."